Four inmates on Oklahoma's death row, including one scheduled to be executed on Thursday, have asked the U.S. Supreme Court to overturn a federal appeals court ruling that approved the state's choice of execution drugs.

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The documents filed Wednesday argue that that the use of midazolam in a three-drug mixture to perform an execution is unacceptable because it cannot reliably produce "a deep, comalike unconsciousness."

The issue of how inmates are executed and whether the existing drug protocols lead to constitutionally prohibited cruel and unusual punishment has been widely debated since a series of executions in which the condemned men seemed to suffer.

After an intravenous line failed on April 29, 2014, Oklahoma inmate Clayton Lockett writhed and gasped for 43 minutes until he died.

In the latest challenge, attorneys for Charles Warner, Richard Eugene Glossip, John Marion Grant and Benjamin Robert Cole requested stays of their scheduled executions pending their appeal of the U.S. 10th Circuit Court ruling.

The prisoners' challenge centers on Oklahoma's use of midazolam, a drug that has been used in several executions in which prisoners initially appeared to lose consciousness but then awakened and struggled before dying.

The Oklahoma case cites the case if Dennis McGuire, who made snorting noises for over 20 minutes during his execution in Ohio in January.

Joseph Wood took nearly two hours to die last year in an Arizona execution. Both executions, along with Lockett's, involved midazolam.

Warner is scheduled to be executed on Thursday, Glossip on Jan. 29, Grant on Feb. 19, and Cole on March 5.

Florida voters opted to automatically restore voting rights to former felons, affecting some 1.4 million residents. In Louisiana, voters instituted a five-year waiting period for felons to seek political office.